Electroluminescent-piezoelectric bar graph display system



H. G. BLANK Aug. 24, 1965 ELECTROLUMINESCENT-PIEZOELECTRIC BAR GRAPH DISPLAY SYSTEM 2 Sheets-Sheet 1 Filed Oct. 24, 1962 VOLTS TIME INVENTOR HANS G. BLANK fi. Fm

A TORNEY Aug. 24, 1965 H. G. BLANK 2 Sheets-$heet 2 REFERENCE GEN 32 COMPARATOR COMPARATOR COMPARATOR COMPARATOR 38 39 [40 4| 1 v R R R R 5 MV MV 5 MV 5 MV DELAY v v DRIVER A GEN I so INVEN'i'OR HANS G. BLANK BY 1% f AT RNEY United States Patent -ELECTROLUMINESCENT-PIEZOELECTREC BAR GRAPH DISPLAY SYSTEM Hans G. Blank, Bronx, N.Y., assignor to General Telephone and Electronics Laboratories, Inc., a corporation of Delaware Filed Oct. 24, 1962, Ser. No. 232,726 5 Claims. (Cl. 315-55) This invention relates to display devices.

Analog display devices, in which information is presented in the form of bar graphs, have potentially wide application in the control of industrial processes, in aircraft instrumentation, and, in general, in the display of a large number of related variables. Many electromechanical devices have been developed for providing bar displays, but these usually have relatively low speeds of response and are bulky and heavy. Electronic devices are also available for performing this function but have the disadvantage that they require sealed glass envelopes operating at low internal pressures.

Accordingly it is an object of my invention to provide an improved bar type display.

It is another object of my invention to provide a display device which may be easily and accurately read and which permits rapid comparison of two or more variables.

Still another object of the invention is to provide a bar type display which has a relatively high speed of response, is compact and light in weight.

Yet another object is to provide a display device utilizing a minimum number of components but which permits the display of a large number of variables.

The present invention is directed toward a panel for displaying a plurality of variables as parallel bars of light. The length of each bar is proportional to the magnitude of the variable being measured.

In one embodiment of the present invention, there is provided a transducing member comprising a sheet of piezoelectric material having first and second surfaces. An elongated driving electrode is affixed to the first surface'of the sheet adjacent one edge and a common electrode is secured to the other surface of the sheet. An electroluminescent layer is afiixed to the first surface of the piezoelectric sheet adjacent the driving electrode. A plurality of spaced transparent input electrodes are secured to the surface of the electroluminescent layer, these electrodes extending in a direction normal to the driving electrode. The edges of the piezoelectric sheet parallel to the driving electrode are provided with terminations which absorb, substantially without reflection, any incident elastic wave.

In another embodiment of the invention, a non-linear resistance layer is interposed between the piezoelectric sheet and the electroluminescent layer. As shall be explained hereinafter, the non-linear resistance layer increases the contrast of the display.

When a voltage step is applied to the driving electrode, a mechanical strain is produced in the piezoelectric sheet which is proportional to the amplitude of the step. This change in strain produces a disturbance in the form of an elastic wave accompanied by an electric field which is propagated at constant speed toward the opposite edge of the sheet. The intensity of the field is proportional to the time rate of change of the strain producing it and, therefore, is proportional to the first time derivative of the applied step. This traveling elec tric field, however, is not of sufiicient magnitude to cause the electroluminescent layer to emit light.

Input voltages are applied to each of the transparent input electrodes, each of these voltages having a duration which is proportional to the magnitude of the variable ice to be displayed. These voltages are applied to the input electrodes at the instant the traveling elastic wave in the piezoelectric sheet reaches the edge of the electroluminescent layer. The sum of the voltage produced by the traveling wave and any one of the input voltages is sufficient to cause the portion of the electroluminescent layer under the excited transparent electrode to emit light.

When each input voltage drops to zero, the portion of the electroluminescent layer still being swept by the electric field propagated in the piezoelectric sheet ceases to emit light because the traveling electric field is of insufficient magnitude to sustain light emission. Since the velocity of wave propagation in the piezoelectric material is a constant, the length of the light emitting portion of the electroluminescent layer under the transparent electrode is proportional to. the duration of the input voltage and hence to the magnitude of the displayed variable.

The above objects of and the brief introduction to the present invention will be more fully understood and further objects and advantages will become apparent from a study of the following description in connection with the drawings, wherein:

FIG. 1 is a perspective view of my display device;

FIG. 2 is a plan view of the display device of FIG. 1 together with a block diagram of the excitation circuits; and

FIG. 3 depicts idealized voltage waveforms useful in explaining the operation of the circuit of FIG. 2.

Referring to FIG. 1, there is shown a thin, rectangular, polarized, ceramic piezoelectric sheet 10 consisting of a lead titanate-lead zirconate mixture. A common grounded electrode 11 is aifixed to one surface of piezoelectric sheet 10 and a non-linear resistance layer 12 is secured to the other surface of the sheet. Layer 12 covers almost the entire surface of sheet 10, a narrow strip 16a along one edge of sheet 10 being left uncovered. The non-linear resistance layer 12 may be of the type disclosed in copending application Serial No. 72,789 filed November 30, 1960, by Stephen Yando consisting of an essentially non-photoconductive cadmium sulfide powder embedded in an epoxy resin. The resistance of this layer decreases as the voltage applied across it increases or, stated another Way, the current through the non-linear resistance layer varies according to the equation IzkV where I is the current through the layer, V is the voltage across it and n is a number greater than 1.

An electroluminescent layer 13 is placed in intimate contact with non-linear resistance layer 12 and 57 mrality of spaced elongated transparent input electrode strips 14, 15, 16 and 17 are afiixed to the top surface of electroluminescent layer 13. While only four electrode strips are shown, it shall be understood that any desired number may be employed.

Edge v18 of non-linear resistance layer 12 and the edge of electroluminescent layer 13 are spaced from the corresponding edge of piezoelectric sheet 10. An elongated driving electrode 19 is secured to strip 10a adjacent edge 18. As shown, input electrodes 14-17 extend in a direction normal to that of driving electrode 19.

The edges of piezoelectric sheet 10 which are parallel to driving electrode 19 are terminated in such manner as to absorb, substantially without reflection, any incident elastic wave propagated in the sheet. This is accomplished by coating the edges and immediately adjacent portions of the sheet with lead to provide terminations 20 and 21.

The application of a voltage step between electrode 19 and grounded electrode 11 causes an elastic wave to be propagated down the piezoelectric sheet 10 at constant speed toward absorbing termination 21. This wave is 3 accompanied by an electric field having an intensity proportional to the time rate of change of the step applied to electrode 19. A reverse wave also emanates from electrode 19 but is absorbed by termination 20 without affecting the display.

The electric field produced by the traveling elastic wave is applied across the electroluminescent and nonlinear resistance layers in series. Due to the high resistance of non-linear layer 12, the current charging the electroluminescent layer 13 is quite low and therefore the voltage appearing across the electroluminescent layer is insufficient'to produce light. When the elastic wave reaches edge 18, voltages are applied between one or I more of the transparent input electrodes 14-17 and ground. The voltage applied to each input electrode adds to the voltage generated by the elastic wave thereby increasing the voltage across the non-linear resistance layer 12. layer 12 causing a large charging current to flow into the portion of electroluminescent layer 13 under the energized input electrode. Thischarging current produces a rapid increase in the voltage across electroluminescent layer 13 and causes it to emit light over the area immediately below the energized electrode.

In operation, a voltage step is applied between terminal 25 of electrode 19 and ground thereby initiating a traveling elastic wave accompanied by an electric field in piezoelectric sheet 10. When this wave reaches edge 18, step voltages are applied to one or more input terminals 26, 27, 28 and 29. As a result, the portions of the electroluminescent layer under the energized electrodes 14-17 emit light as shown by the shaded areas in FIG. 1. The durations of the voltages applied to terminals 26-29 are made proportional to the magnitudes of the input variables and consequently, the length of each bar is proportional to the magnitude of the input variable. When the voltage on any of input terminals 26-29 drops to zero the portion of electroluminescent layer 13 under the corresponding electrodes 14-17 ceases to emit light. This is because, as previously explained, the voltage provided by the elastic wave alone is insulficient to produce light in the electroluminescent layer.

In some applications, where the non-linearity of electroluminescent layer 13 is sufficient, non-linear resistance layer 12 may be omitted. Greater brightness is thereby obtained from the display although the contrast may be somewhat decreased.

FIG. 2 is a block diagram of the apparatus used in presenting input information on the display device in the form of lighted bars having lengths proportional to the magnitudes of the input variables. Although all of the blocks are illustrated as connected by a single lead, it will I be understood that each component is connected to a common ground point and that all voltages are measured with respect to this ground.

FIG. 3 shows voltage waveforms existing at the points designated by A-H in FIG. 2.

Referring to FIGS. 2 and 3, a driver generator 30 is coupled directly to terminal 25 of driver electrode 19. Generator 30 produces a sawtooth-shaped voltage waveform at point A having a first step portion in which the magnitude of the sawtooth changes'rapidly over a period T and a second portion in which the magnitude changes slowly over a recovery period T,-. Since the electric field generated in piezoelectric sheet is proportional to the rate of change of the applied voltage, it is the voltage applied to electrode 19 during the period T which produces the elastic wave in the sheet. The slowly changing portion of the sawtooth during the interval T does not give rise to a traveling wave, this portion being the recovery period of the generator.

The output of driver generator 30 is coupled through a delay circuit 31 to a reference generator 32 which produces a sawtooth voltage output as shown at B in FIG. 3. The start of the sawtooth is delayed by delay circuit 31 This increased voltage decreases the resistance of v 4 for an interval equal to the time it takes the elastic wave to travel from electrode 19 to'the edge 18 of non-linear resistance layer 13. The delayed output of driver generator is also connected to the SET inputs S of pulse generators 33, 34, 35, and 36 by means of a lead 3'7. Pulse generators 33-36 may be multivibrators of the type disclosed in FIG. 1.1, page 10 of the book Switching Circuits with Computer Applications by Watts S.

Humphrey, published by McGraw-Hill Book Co. in 1958. These generators have a first or SET input which initiates the output'pulse when-energized and a second or RESET input R which terminates the output pulse when energized. As a result, pulses are applied to input terminals 26-29 by multivibrators 33-35 simultaneously with the triggering of reference generator 32. The pulses generated by multivibrators 33 and 34 are shown at E and H' in FIG. 3.

The output of reference generator 32 is coupled to comparator circuits 38, 39, 40 and 41. Comparators 38-41 may be of the type employing two input and one output connection as shown in FIGS. 9-6, page 332 of the book Waveforms by Chance et al., publishedby McGraw-Hill Book Co. When the two input voltages in this circuit are equal, an output voltage pulse is initiated which continues at constant magnitude until one of the inputs is reduced to zero. Thus, comparators 38-41 I each produce an output pulse whenever a signal applied to a corresponding one of terminals 42, 43, 44 or 45 is equal to the magnitude of the sawtooth output voltage B of reference generator 32. The output of each of the comparators 38-41 is coupled to the RESET input of the corresponding multivibrators 33-36, theoutputs of the magnitude of the sawtooth reference voltage reaches a value a (see FIG. 3B), the comparator 38 generates a pulse FIG. 3D) which ends when the reference sawtooth falls to zero. The leading edge of the comparator output pulse D resets multivibartor 33 reducing its output pulse E to zero. Since the rate of rise of the reference sawtooth B is linear, the duration of the pulse E applied to terminal 26 of electrode 14 is proportional to a. Thus, the length of the light emitting portion of electroluminescent layer 13 immediately under electrode 14 is also proportional to the magnitude of the input variable. A smaller input voltage F having a magnitude b is shown applied to terminal 43 of comparator 39. Since this voltage is smaller in magnitude than C, the comparator output voltage is initiated earlier in the cycle resulting in the waveform shown in FIG. 3G. The earlier initiation of the comparator voltage resets multivibrator 34 earlier resulting in a relatively short pulse (FIG. 3H) being applied to terminal 27 of electrode 15. The location of this pulse, and therefore, the length of the light emitting portion of electroluminescent layer 13 under electrode 15, is proportional to the signal voltage b. Similarly, other signals may be applied 7 to electrodes 16 and 17 to display additional input variables as 'bars of light.

Ina typical device of the type described, the electrodes 14-17 are about 4 inches in length, the frequency of the driver generator 311 about 10 kilocycles per second,

and the velocity of the elastic wave in piezoelectric sheet 10 approximately -inch per microsecond. Thus it requires 28 microseconds for the elastic wave to travel from one end of the electroluminescent layer to the other and, therefore, the duration T of the reference sawtooth voltage (FIG. 3B) is about 28 microseconds.

Although only a single driver electrode 19 has been shown, it shall be understood that a plurality of parallel spaced driver electrodes might also be used as described 5 in the copending application Serial No; 183,229 filed March 28, 1962, by Stephen Yando.

As many changes could be made in the above described construction and many different embodiments could be made Without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A device for displaying a plurality of input signals as illuminated bars comprising (a) a sheet of piezoelectric material having first and second surfaces and at least one edge,

(b) an electroluminescent layer having first and second surfaces, the second surface of said electroluminescent layer being afi'ixed to the first surface of said sheet,

(c) an elongated driving electrode secured to the first surface of said sheet between said electroluminescent layer and the edge of said sheet,

(d) common electrode means secured to the second surface of said sheet, and

(e) a plurality of spaced transparent input electrodes secured to the first surface of said electroluminescent layer, said input electrodes extending in a direction normal to said driving electrode.

2. A device for displaying a plurality of input signals as illuminated bars comprising (a) a sheet of piezoelectric material having first and second surfaces and first and second parallel edges,

(b) an electroluminescent layer having first and second surfaces,

(c) a non-linear resistance layer interposed between the first surface of said sheet and the second surface of said electroluminescent layer, said electroluminescent layer and said non-linear resistance layer being spaced from the first edge of said sheet,

(d) elongated driving electrode means secured to the first surface of said sheet in the space adjacent said electroluminescent and non-linear resistance layers, said elongated driving electrode means extending in a direction parallel to said first edge of the sheet,

(e) common electrode means secured to the second surface of said sheet,

(f) a plurality of spaced elongated input electrodes secured to the first surface of said electroluminescent layer, said input electrodes extending in a direction normal to said driving electrode means, and

(g) first and second termination means afiixed to the first and second edges of said sheet respectively, said termination means absorbing substantially without reflection any incident elastic Wave supplied thereto from said sheet.

3. A display device comprising (a) a sheet of piezoelectric material having first and second surfaces and first and second parallel edges,

(b) an electroluminescent layer affixed to the first surface of said sheet, said electroluminescent layer being spaced from the first edge of said sheet,

() driving electrode means secured to the first surface of said sheet in the space adjacent said electroluminescent layer said driving electrode means extending in a direction parallel to said first edge of the sheet, 7

(d) common electrode means secured to the second surface of said sheet,

(e) means for applying a driving voltage between said driving electrode means and said common electrode means, said means including a driver generator coupled between said driving electrode means and said common electrode means,

(f) a plurality of spaced elongated input electrodes secured to the surface of said electroluminescent layer, said input electrodes extending in a direction normal to said driving electrode means, and

(g) means for applying input voltage pulses between each of said plurality of spaced input electrodes and said common electrode means, each of said means including a pulse generator having first and second inputs and an output, said first input being coupled to the output of said driver generator and the output of said pulse generator being coupled to a corresponding one of said input electrodes; and a comparator circuit having a first input adapted to receive a reference signal, a second input adapted to receive an applied input signal and an output coupled to the second input of said pulse generator, said comparator circuit generating an output pulse when the magnitude of said reference signal equals the magnitude of said input signal, said pulse generator applying an output pulse to said corresponding input electrode a predetermined interval after said driver generator applies a pulse to said driving electrode and terminating said pulse When the output of said comparator circuit is applied to the second input of said pulse generator.

4. A display device comprising (a) a sheet of piezoelectric material having first and second surfaces and first and second parallel edges,

(b) an electroluminescent layer afiixed to the first surface of said sheet, said electroluminescant layer being spaced from the first edge of said sheet,

(c) driving electrode means secured to the first surface of said sheet in the space adjacent said electroluminescent layer 5 said driving electrode means extending in a direction parallel to said first edge of the sheet,

(d) common electrode means secured to the second surface of said sheet,

(e) means for applying a driving voltage between said driving electrode means and said common electrode means, said means including a driver generator coupled between said driving electrode means and common electrode means,

(f) a plurality of spaced elongated input electrodes secured to the surface of said electroluminescent layer, said input electrodes extending in a direction normal to said driving electrode means,

(g) a plurality of pulse generators each having first and second inputs and an output coupled to a corresponding input electrode, the first input of each of said pulse generators being coupled to the output of said driver generator,

(h) a plurality of comparator circuits each having first and second inputs and an output coupled to the second input of a corresponding pulse generator, and

(i) a sawtooth reference generator having an output coupled to the first inputs of each of said comparator circuits, each of said comparator circuits applying a voltage to the second input of the corresponding pulse generator when the magnitude of the output of the reference generator equals the magnitude of a signal applied to the second input of said comparator circuit, each of said pulse generators applying a signal to the corresponding input electrode When its first input is energized by said driver generator and terminating said pulse when its second input is energized by the output of said comparator circuit.

5. A display device as defined by claim 4 wherein delay means couples the first inputs of said plurality of pulse generators to the output of said driver generator and the input of said reference generator to the output of said driver generator, said delay means providing a delay equal to the time required for an elastic wave to travel through said sheet of piezoelectric material from said '2 drivar electrode to the adjacent edge of said elcctro- 3,054,929 luminescent layer. 3,072,821 .1. v, 1 3 121 24 1 Referen cgs Cited by the Examiner 3 132 27 UNITED STATES PATENTS 5 2,877,371 3/59 Orthuber et a1. 313-108 2,951,168 8/60 Yando 31555 X LivingstCn 5 315-169 Yando BIS-55 Talesnick 315169 Yando 315 -55 GEORGE N. WESTBY, Primary Examiner. JOHN W. HUCKERT, Examiner. 

1. A DEVICE FOR DISPLAYING A PLURALITY OF INPUT ISGNALS AS ILLUMINATED BARS COMPRISING (A) A SHEET OF PIEZOELECTRIC MATERIAL HAVING FIRST AND SECOND SURFACES AND AT LEAST ONE EDGE, (B) AN ELECTROLUMINESCENT LAYER HAVING FIRST AND SECOND SURFACES, THE SECOND SURFACE OF SAID ELECTROLUMINESCENT LAYER BEING AFFIXED TO THE FIRST SURFACE OF SAID SHEET, (C) AN ELONGATED DRIVING ELECTRODE SECURED TO THE FIRST SURFACE OF SAID SHEET BETWEEN SAID ELECTROLUMINESCENT LAYER AND THE EDGE OF SAID SHEET, (D) COMMON ELECTRODE MEANS SECURED TO THE SECOND SURFACE OF SAID SHEET; AND (E) A PLURALITY OF SPACED TRANSPARENT INPUT ELECTRODES SECURED TO THE FIRST SURFACE OF SAID ELECTROLUMINESCENT LAYER, SAID INPUT ELECTRODES EXTENDING IN A DIRECTION NORMAL TO SAID DRIVING ELECTRODE. 